Upcoming generations of wireless communication systems, such as Fifth Generation (5G) communication systems, are expected to enable applications such as virtual reality, augmented reality, reliable remote operation of machines, factory automation, network-assisted control of traffic and self-driving vehicles, and the cellular “Internet of Things (IoT)” that supports internetworking of physical devices such appliances, vehicles, buildings, and other items that are embedded with electronics, software, sensors, actuators, and network connectivity that enable the devices to collect and exchange data over the Internet. Future 5G communication systems will therefore be required to support gigabit per second data rates (e.g., to support virtual or augmented reality applications), end-to-end latencies of at most 10 milliseconds (ms) (e.g., to support factory automation applications), reliabilities of at least 99.999% (e.g., for automotive traffic control applications such as platooning), and user equipment densities of tens of millions of devices per square kilometer (e.g., to support cellular IoT applications).
The radio interface defined by current 4G standards is not able to meet the requirements set out for future 5G communication systems. For example, the system bandwidth and multiple antenna configuration options specified in the 4G standards are not able to provide gigabit per second data rates for large numbers of users. For another example, the frame structure defined by the 4G standards, as well as the random access, control signaling, retransmission, and scheduling mechanisms in the 4G standards are not designed to support end-to-end latencies of 10 ms or less. For yet another example, modulation and coding schemes, antenna configuration options, network connectivity options, and receiver algorithms set forth in the 4G standards are not designed to provide 99.999% reliability. For yet another example, the techniques for pairing or scheduling of user equipment, pilot symbols such as demodulation reference signals, power control mechanisms, random access mechanisms, control signaling, antenna configuration options, and receiver algorithms specified by the 4G standards are not able to support concurrent communication with devices at the densities required by IoT applications.